Thread: UPS ?
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Old February 21st 18, 09:15 PM posted to alt.comp.hardware
philo
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Default UPS ?

On 02/21/2018 11:21 AM, Paul wrote:
philo wrote:

Thanks Paul.

It seems to be something to do with the mobo's behavior with a PSU
other than the original.

The mobo has a 20 pin power connection and the original supply had a
24 pin connection (with the 4 pin connector left dangling of course.)

I replaced it with a simple 20 pin PSU


I know that there the 20 pins of a 24 pin PSU are somehow a bit
different than that of a straight 20 pin PSU because when I test 24
pin supplies with my 20 pin tester, one of the red warning lights goes
on even though the supply is good.


The four leftover pins on the 24 pin are for "ampacity". You might not
find that in your dictionary, and some staff at work introduced me
to the (apparently made up) word.

There is no functional difference as such between 20 and 24 pins.
The 24 pins, the actual useful benefit, is the additional yellow
+12V wire, which was badly needed. That raises the current available
for PCIe slots from 6A to 12A. Before the 24 pin came along, some
companies were putting a 4 pin Molex on the motherboard, to carry
a bit more current for +12V.

There are two tables here, you can use to compare a 20 pin to
a 24 pin. The difference, the extra four pins, look like this.

http://www.playtool.com/pages/psucon...onnectors.html

Description ColorÂ*Â* PinÂ*Â* PinÂ* ColorÂ* Description

+12 voltsÂ*Â* yellowÂ* 11Â*Â*Â* 23Â*Â* redÂ*Â*Â* +5 volts
+3.3 voltsÂ* orangeÂ* 12Â*Â*Â* 24Â*Â* blackÂ* ground

There are already a fair number of 3.3V, 5V, and Ground wires
so adding one more of each isn't as big an improvement, as that
Yellow wire for +12V is.

The worst card for slot power, was a 6600 video card, with 4.2A
of 12v slot power. Two of those would exceed the conservative 6A
limit for the single Yellow wire on the 20 pin. You could safely
run two 6600 cards on a 24 pin connector, as the 12A available,
exceeded the 8.4A load.

When you buy a $1000 video card, those only draw around 2A from
the slot. It's the mid-range cards, the one without a PCIe power
connector on the end, that push towards the slot limit of 12V @ 5A max.

It's really hard to guess where the 3.3V and 5V current flow
levels are today. But you'll notice that the "gigantic" modern
80+ supplies only offer 20A on 3.3V and 5V. And it is hard to
get a supply with more (there are traditional design PSUs that
go up to 40A on the low rails).

Some video cards have used as much as 3A on the 3.3V, so two video
cards would be 6A out of 20A.Â* And the chipset is pretty thirsty
and could well be running from the wrong rail as well. There will
be some things that can run directly from 3.3V. And a lot of lower
voltages (1.2, 1.5, 1.0V) that you could run off 12V if you had the
ampacity to do it. Switching regulators (like the switching supply for
the DIMMs) get less efficient at lower voltages (but that's never
stopped anyone in the past).

With the "sleeved" cables of modern supplies, I can't get my
ammeter jaws around stuff, to characterize my newer machines.
And the new machine, the heatsink is so big, I can't even get
my hands inside to seat half of the DIMMs, and have to snap
them into place with a sort of dowel to press down on them.
Not the nicest place to be doing power testing. No room
for anything. And spinning fan blades to nick me if I get
too adventurous (VCore has a fan on it now).

Â*Â* Paul






I am familiar with the portmanteau"ampacity" but shy away from using the
term.

It too much reminds me of laymen who use the term "amperage" rather
than "current."



At any rate, I decided to have a look at all the spare power supplies I
have in my workshop and the older 20 pin supplies have a white (-5v)
wire at pin 18.

My tester which is evidently ancient gives all green lights on those
supplies.

I have some newer 20 pin supplies which do not have that white wire
which corresponds to the "missing" wire at pin 20 on the 24 pin supplies.


My tester gives an over-all fault (red) for those supplies but all other
green lights are lit up but one.


Now that I have the machine all put back together and working I don't
think I'll fool with it anymore, but one of these days when I get a
chance I'll see what can cause a fault on that old Patriot UPS I have.



Though I always use 24 pin supplies with 24 pin motherboards, in this
case, since the mobo was just 20 pin, I figured it would be a good way
to use up one of my old, 20 pin supplies.